The United States is the biggest jailer in the world, with 5 percent of the global population but 25 percent of its prisoners, as the president noted in a statement to the press at El Reno. The Bureau of Justice Statistics (BJS) finds more than 2.3 million people sit in federal, state or local prisons and jails. Close to 7 million Americans are under adult correctional supervision, a number that includes people in jail, on parole or on probation.

How did the United States develop a criminal justice system that relies so heavily on incarceration? Explore the history of American correctional system in this slideshow.

Mary Dyer was exiled by Massachusetts authorities over a theological dispute. She returned and was arrested three more times by authorities for spreading Quakerism. On the fourth arrest, she was executed. |
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Prior to the 18th century, the concept of prison or jail as a means of punishment didn't exist in the Europe or its American colonies. Jails did exist, but they were a means of holding criminals temporarily until a trial or punishment could be meted out. Political prisoners and debtors were the only ones who saw any kind of extended stay.

Religious, civil and criminal infractions would all be undertaken by the justice system. Punishment came in the form of public shaming, flogging, exile or execution. In fact, many early arrivals to the American colonies were criminals banished from England. Up until 1776, it was standard procedure for British authorities to banish criminal offenders to the American colonies as a form of punishment. That practice ended after the Revolutionary War, and Australia took the place as the primary destination for British convicts.

William Penn, founder of Pennsylvania, was an early champion of prison reform, and was himself incarcerated several times because of his religion. |
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Just because colonial authorities didn't rely on jails for punishment doesn't mean they weren't an essential addition to early settlements. As the Colonial Williamsburg Foundation notes, some of the earliest buildings erected in what would be the United States were prisons. Back when the city of Boston was little more than a village of 40 homes, settlers still felt the need to construct a jail.

As settlements expanded in size and trade blossomed to support a growing economy, crime increased as well. The English legal system responded to this trend with what was known as "The Bloody Code," which grew the number of capital crimes from around 50 to over 200.

Americans who were uncomfortable with the increased reliance in capital punishment sought an alternative. The writings of Cesare Becarria, John Howard and other penal reformers provided the philosophical underpinnings for a new way of thinking about criminal law. Quakers in Pennsylvania and West Jersey were among the first to advocate substituting corporal or capital punishment for imprisonment, laying the foundations of modern criminal justice.

Old Newgate Prison was a colonial American prison that originally opened as a copper mine. Its first prisoner arrived in 1773 and escaped 18 days later. Considered costly and inhumane even for its time, the prison closed in 1827. |
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After the Revolutionary War and into the 19th century, a combination of low mortality rates and high levels of immigration led to a population boom in the newly created United States. Over a four-decade period, states more than doubled in population. Between 1790 and 1830, the number of New York residents soared five-fold.

This population growth put a major strain on the prison system, lacking in both infrastructure and decency. Resource constraints led to overcrowding, which in term led to ineffective and often cruel prison policy, a cycle that would repeat itself throughout U.S. history. Ramshackle facilities, deplorable hygiene and rampant corruption plagued early prisons. Again led by the Quakers, early reformers pushed for improved in prisoner conditions that guaranteed a healthy and reasonably dignified incarceration.

In 1831, Alexis de Tocqueville and Gustave de Beaumont, the French political observers and historians responsible for the landmark work "Democracy in America," arrived in the midst of the nation's first-ever prison building boom (PDF). The Frenchmen noted that what separated the conditions of the facilities across the cities and towns of mid-19th century America was money, as well-equipped prisons and jail were a luxury in their time.

Walnut Street Jail was considered a model for its time, a progressive institution touted by prison reform advocates. |
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In order to offset the costs of their housing, prisoners in workhouses, jails or prisons often had to labor in the facilities to which they were incarcerated in roles that were often hard labor.

Work was also seen as a privilege for prisoners and essential to helping them rehabilitate and once reenter society. At the Walnut Street Jail in Pennsylvania, established in 1790, most offenders housed there worked together making clothing or shoes. The most serious criminals were kept in solitary confinement, allowed only a Bible.

Eastern State Penitentiary isolated prisoners, preventing any form of communication among one another, in order to encourage reflection and rehabilitation, according to its architects. |
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As de Tocqueville noted in "Democracy in America," the various legal jurisdictions allowed for experimentation in the justice system and how prisoners were treated. One system developed in Auburn prison in 1821 enforced strict silence and hard labor, backed by corporal punishment for any prisoners acting out.

The main rival to the Auburn system among corrections authorities was the one developed at Eastern State Penitentiary, the largest and most expensive such facility at the time of its construction in 1829. Prisoners were kept entirely separate from one another, and had their own sleeping, bathing and exercise facilities, all within a single cell.

Both systems operated under the idea that prisoners' behavior could be reformed through either solitary confinement or labor. "Penitent" prisoners would be kept in a "penitentiary." Because of the expense associated with Eastern's form of incarceration, prison facilities were more likely to align with the Auburn system.

African Americans were arrested and their labor leased to private businesses, a form of punishment that endured well into the 20th century. |
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The mid-19th century brought profound demographic changes to the United States. The defeat of the Confederacy in the Civil War led to the emancipation of millions of African-American slaves in the South. Waves of immigrants arrived at the shores of American industrial cities looking for work. Others migrated West in search of a new life.

As was the case with the newly independent United States, post-Civil War America experienced a rise in crime rates, which led to prison overcrowding. As in the 18th-century, overcrowding lead to decay and corruption. In order to exert some form of control of their convicts, many Northern prisons reverted back to corporal punishment for prisoner infractions, a practice that would continue both officially and unofficially until well into the 20th century.

In the South, newly freed slaves often found themselves back in chains over the most minor offenses. Black prisoners quickly became a disproportionate number of the total prison population as they were targeted by law enforcement authorities and given heavy sentences by a racially biased justice system.

The Thirteenth Amendment made slavery illegal, but arresting criminals, sentencing them to hard labor and then leasing that labor was all perfectly legal. This marked the beginning of the convict lease system, in which prisoners in the custody of the state were leased to private enterprises. Once again, involuntary labor was big business in the South, though Northern institutions weren't above taking advantage of this lucrative opportunity either.

Because of the conditions in which prisoners were kept, injuries and even death from the physical discipline, essentially torture, were commonplace. Some prison camps saw mortality rates as high as 40 percent.

Alcatraz, one of the most infamous maximum security prisons in U.S. history, opened in 1934. Given that the facility was once a former military prison and housed on a remote island, the institution clearly existed as a means of punishment and isolation, rather than prisoner reformation. |
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In the late 19th century and early 20th century, women's-only prisons and juvenile facilities began to emerge. Many of the reforms that improved quality of life for inmates, such as vocational training, educational classes, libraries and recreation, can be credited to innovations pioneered in women's prisons.

As cities grew larger at the turn of the century, prisons expanded and inmate populations swelled. The 20th century saw the creation of the first maximum security facilities.

The 20th century also marked a clear shift in penal policy from prisons being correctional facilities to institutions built maintain social order and isolate unwanted individuals. This attitude led most prison facilities to be constructed in remote, rural areas rather than the cities from which most inmates originated.

Prison work laws also changed, largely as a result of the Great Depression. With high unemployment, the idea that convict labor could compete with free workers proved politically unpopular. This left prison officials reliant on state and federal grants to keep their facilities running.

U.S. prison history shows cycles of overcrowding and overspending followed by reform. |
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Throughout the first half of the 20th century, the U.S. prison population remained steady. Beginning in at least the late 1970s, the number of prisoners held in local, state or federal saw a sharp trend upward.

In 1978, the state and federal prison population was less than 350,000 members. More than 1.5 million inmates were housed in these facilities 25 years later. Similarly, state expenditures on corrections has increased from $6.5 billion spent in 1985 to $51.9 billion in 2013.

Primary contributors to this prison boom have been tough-on-crime policies, particularly those focused on drug possession and trafficking, mandatory minimums, "three strikes" laws and other measures that have led to a state in which 1 in 31 U.S. adults is behind bars, on parole or on probation, according to the Pew Center for the States. These policies have also led to a disproportionate number of minorities being put behind bars, with African Africans representing 40 percent of the total prison population, even though they are 13 percent of the U.S. population.